Deeper you go,the partial pressure of CO² increases and worsens the symptoms with minimuns increases.For a while,we can´t address the narc effects of all breathed gases separately,but the net sum can be lethal.Some rebreathers have electronic gauges that can warn about EXALED PCO²,not from the blood,at least it helps not to get into a danger zone.It helped anesthesiologists to monitor the surgical patient in an or but they know it can´t be the only consideration and blood gasimetric measures are most the accurate for biochemical corrections...and they are in a hospital among many specs around for helping hand.